OBJECTIVES: We examined whether schoolyard improvements led to increased physical activity levels among both boys and girls and assessed the aspects of schoolyard design that have an impact on physical activity.  METHODS: In a quasi-experimental research design, 6 schools with renovated schoolyards and 3 control schools were divided into activity areas. We calculated measures of children's physical activity by area during school hours as well as after-school hours. RESULTS: The volume of schoolyard use was significantly higher at schools with renovated schoolyards than at control schools, and students were significantly more active at these schools. Also, activity levels were significantly higher among both boys and girls in certain schoolyard areas, such as those with soft surfaces. CONCLUSIONS: Because few public elementary schools in the United States provide daily physical education or its equivalent for all students throughout the school year, noncurriculum approaches to increasing children's physical activity are important. Renovated schoolyards increase the number of children who are physically active, as well as their overall activity levels, and reduce sedentary behaviors.